This invention relates to shaving devices and concerns a safety razor blade unit having at least one blade with a cutting edge which is moved across the surface of the skin being shaved by means of a handle to which the blade unit is attached. The blade unit may be mounted detachably on the handle to enable the blade unit to be replaced by a fresh blade unit when the blade sharpness has diminished to an unsatisfactory level, or it may be attached permanently to the handle with the intention that the entire razor be discarded when the blade or blades have become dulled. Razor blade units generally include a guard which defines a surface for contacting the skin in front of the blade(s) and a cap for contacting the skin behind the blade(s), the cap and guard serving important roles in establishing the so-called xe2x80x9cshaving geometryxe2x80x9d, i.e. the parameters which determine the blade orientation and position relative to the skin during shaving. The present invention is especially concerned with the guard structure of a razor blade unit.
It is known to include in a guard structure an elastomeric strip with a surface configuration intended to produce pleasant tactile sensations on contact with the skin during shaving, for example as described in U.S. Pat. No. 5,191,712, and/or to interact with the hairs in a favourable manner immediately before they are cut by a blade of the blade unit moving across the skin and following the guard structure. The surface configuration of the elastomeric strip can take a variety of different forms, including upstanding discrete projections e.g. tubes or crescent-shaped projections, or fins either extending parallel to the blade edge or transverse thereto. A form of elastomeric strip incorporated in currently marketed blade units has a series of, e.g. 4 or 5, parallel fins extending lengthwise of the blade unit. The present invention is particularly described herein with reference to a strip of this latter form, and to an alternative strip construction incorporating upstanding tubes of D-shape cross-section, but it should be understood that the invention is equally applicable to guard structures with elastomeric strips with any other surface configuration for interaction with the skin and/or hairs. Other forms of elastomeric strip are described for example in U.S. patent application Ser. No. 09/113,460, filed Jul. 10, 1998 (which corresponds to WO97/25190) and U.S. patent application Ser. No. 09/141,436, filed Aug. 27, 1998, issued as U.S. Pat. No. 6,298,557 (which corresponds to WO97/33729), the contents of which are incorporated herein by reference.
When an elastomeric strip is included in the guard structure of a razor blade unit it is usual to provide between the elastomeric strip and the adjacent blade edge a so-called xe2x80x9cbackstopxe2x80x9d which is a rigid part having an upper surface for contact with the skin. The backstop is important in establishing certain parameters of the geometry, most notably the exposure of the blade, or the leading blade where two or more blades are incorporated in the blade unit. The blade exposure is the distance by which the blade projects beyond a plane which is tangential to the skin contacting surfaces immediately in front of and behind the blade edge. It is well known to provide a blade unit with moving parts so that the blade geometry is dynamically modified during shaving. For example, a blade can be mounted to move in response to forces exerted on the blade during shaving. It is also known to arrange for the rigid backstop to move downwardly under forces exerted on it by the skin during shaving so that the blade exposure tends to increase as load forces imparted on the guard structure increase. However, the need to mount the backstop movably in the housing or frame of the blade unit, and the need to provide return springs to urge the backstop to a normal rest position, complicate the blade unit manufacture and increase production costs.
In accordance with one aspect of the present invention there is provided a guard structure for a safety razor blade unit which has a rigid plastic housing to provide support for at least one blade and a cap structure, the guard structure including; a strip of elastomeric material; and a backstop disposed between the elastomeric strip and a leading blade edge, the backstop comprising a deformable portion capable of yielding resiliently under forces experienced during shaving. Most conveniently the deformable portion is integral with the elastomeric strip. It is preferred that the deformable portion is supported against displacement in a direction towards the leading blade edge by a rigid part of the backstop, which rigid part can be integral with the blade unit housing and may have the form of a wall with a front face and a top face adjoining the front face, the deformable portion being located above the top face and being connected to the elastomeric strip by a part extending upwardly in contact with at least an upper portion of the front face of the wall.
The deformable portion may be arranged to yield by being compressed, for example between the rigid wall and the skin being shaved. In a presently preferred construction, however, the deformable portion yields by flexing. More especially the deformable portion comprises a lip supported at a forward edge thereof and free to flex downwardly under shaving forces. The lip extends rearwardly from an upwardly directed support portion which connects the lip to the elastomeric strip, the trailing edge of the lip being free. Downward deflection of the lip is limited by a stop which is conveniently defined by the rigid wall of the blade unit housing.
By the invention all the benefits of a movable backstop can be secured without the disadvantages of having to provide a moving rigid part and return springs.